1. Field
The present application relates to emissive ceramic materials having phosphor components.
2. Description
Solid state light emitting devices such as light emitting diode (LED), organic light emitting diode (OLED) or sometimes called organic electroluminescent device (OEL), and inorganic electroluminescent device (IEL) have been widely utilized for various applications such as flat panel display, indicator for various instrument, signboard, and ornamental illumination, etc. As the emission efficiency of these light emitting devices continues to improve, applications that require much higher luminance intensity, such as automobile headlights and general lighting, may soon become feasible. For these applications, white-LED is one of the promising candidates and have attracted much attention.
Currently, most light emitting diodes include yttrium aluminum garnet (YAG)-based powders encapsulated in a resin. Increasing the dopant concentration in these powders can obtain white light with improved color temperature. For example, increasing Ce dopant in YAG can increase re-absorption of yellow light, which provides red-shifting that improves the color temperature. Although this strategy can be successful with powders, many light emitting diodes include a transparent ceramic plate or laminated film that will not produce red-shifting when increasing the dopant concentration. The ceramic plates or laminated films fail to re-absorb yellow light because they exhibit high transparency and low scattering.
U.S. Pat. No. 7,390,684 which is hereby incorporated by reference in its entirety, uses a phosphor powder, where Gd can be substituted for Y at less than 20 atomic %. Although this substitution can result in colors with a greater green component, the composition exhibits a significant decrease in luminescence with increased Gd content.